# Merge Data Into Fields

> Fill a DOCX invoice template in Windows Forms with MergeJsonData: import its fields with LoadSettings, merge in a ServerTextControl and save the result as PDF.

- **Product:** TX Text Control .NET for Windows Forms
- **Section:** Documentation
- **Kind:** Topic
- **Path:** TX Text Control .NET for Windows Forms > Getting Started > Mail Merge > Merge Data Into Fields
- **1931 words**
- **Web URL:** https://docs.textcontrol.com/tx-text-control-dotnet-winforms/getting-started/mail-merge/fields/
- **LLMs URL:** https://docs.textcontrol.com/tx-text-control-dotnet-winforms/getting-started/mail-merge/fields/llms.txt
- **LLMs-Full URL:** https://docs.textcontrol.com/tx-text-control-dotnet-winforms/getting-started/mail-merge/fields/llms-full.txt

---

With a template and data in place, `MailMerge` replaces every merge field with the value of the same name and produces the finished document. Here the invoice template from [Create a Template](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/getting-started/mail-merge/template/llms-full.txt) is merged with *invoice.json*, the result is shown in the editor and saved as PDF, and your code finds out which fields received no data.

### Prerequisites

- The application from [Create a Template](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/getting-started/mail-merge/template/llms-full.txt), with the template *invoice.docx* and the data *invoice.json* in the output folder.
- A `Button` named `mergeButton` on the form. Double-click it in the designer to create its `Click` handler.

Add these `using` directives to *Form1.cs*:

```csharp
using System.Collections.Generic;
using TXTextControl.DocumentServer;
```

### How a Merge Works

[MailMerge](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/reference/txtextcontrol-documentserver/mailmerge/llms-full.txt) holds no document itself. Its [TextComponent](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/reference/txtextcontrol-documentserver/mailmerge/textcomponent-property/llms-full.txt) property connects it to a `ServerTextControl` or a `TextControl` that contains the template. A merge method replaces the merge fields with the data, and afterward the connected component contains the merged document.

In this tutorial, the merge runs in a `ServerTextControl`, so that the template in the editor is not touched. The merged document is then shown in the editor.

### Merge the Data

```csharp
private void mergeButton_Click(object sender, EventArgs e)
{
    List<string> fieldsWithoutData = new List<string>();
    byte[] result;

    using (ServerTextControl tx = new ServerTextControl())
    {
        // Initialize the new instance before using it
        tx.Create();

        // Import the MS Word merge fields and merge blocks of the DOCX template
        LoadSettings loadSettings = new LoadSettings
        {
            ApplicationFieldFormat = ApplicationFieldFormat.MSWord,
            LoadSubTextParts = true
        };

        tx.Load("invoice.docx", StreamType.WordprocessingML, loadSettings);

        using (MailMerge mailMerge = new MailMerge { TextComponent = tx })
        {
            // Note every merge field that received no data
            mailMerge.FieldMerged += (s, args) =>
            {
                if (!args.Merged && args.MailMergeFieldAdapter is MergeField mergeField)
                {
                    fieldsWithoutData.Add(mergeField.Name);
                }
            };

            // Replace the merge fields with the values of the JSON data
            mailMerge.MergeJsonData(File.ReadAllText("invoice.json"));
        }

        // Save the result as PDF, and for the editor
        tx.Save("invoice.pdf", StreamType.AdobePDF);
        tx.Save(out result, BinaryStreamType.InternalUnicodeFormat);
    }

    // Show the merged invoice in the editor
    textControl1.Load(result, BinaryStreamType.InternalUnicodeFormat);

    if (fieldsWithoutData.Count > 0)
    {
        MessageBox.Show(this, "No data for: " + string.Join(", ", fieldsWithoutData));
    }
}
```

The code works as follows:

- **Loading the template.** A DOCX template keeps its merge fields as MS Word fields. [ApplicationFieldFormat](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/reference/txtextcontrol/loadsettings/applicationfieldformat-property/llms-full.txt) set to `MSWord` imports them as fields, and [LoadSubTextParts](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/reference/txtextcontrol/loadsettings/loadsubtextparts-property/llms-full.txt) imports the merge blocks of the next tutorial. Without these settings, the fields are not imported as fields.
- **Connecting.** `TextComponent = tx` connects the `MailMerge` to the `ServerTextControl` that holds the template.
- **Merging.** [MergeJsonData](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/reference/txtextcontrol-documentserver/mailmerge/mergejsondata-method/llms-full.txt) takes a JSON string with one object or an array of objects with the same structure. Each field is replaced with the value of the property of the same name. With several objects, the results are combined into one document.
- **Fields without data.** [FieldMerged](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/reference/txtextcontrol-documentserver/mailmerge/fieldmerged-event/llms-full.txt) occurs for each merged field. Its [Merged](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/reference/txtextcontrol-documentserver/mailmerge-fieldmergedeventargs/merged-property/llms-full.txt) property is `false` when the field received no data.
- **The result.** The `ServerTextControl` now contains the merged invoice. It is saved as *invoice.pdf* and handed to the editor as a byte array.

Press **F5** and click **mergeButton**. The editor shows the invoice with *Contoso Ltd.*, *Jane Miller* and *INV-1001* in place of the fields, and *invoice.pdf* is in the output folder.

### Control Empty Fields and Lines

Properties of `MailMerge` decide what happens when the data has no value for a field: [RemoveEmptyFields](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/reference/txtextcontrol-documentserver/mailmerge/removeemptyfields-property/llms-full.txt), `true` by default, removes such fields, and [RemoveEmptyLines](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/reference/txtextcontrol-documentserver/mailmerge/removeemptylines-property/llms-full.txt), `false` by default, also removes lines that are empty after the merge. Set them before calling the merge method.

### Other Kinds of Data

`MailMerge` has a merge method for each kind of data: [Merge](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/reference/txtextcontrol-documentserver/mailmerge/merge-method/llms-full.txt) for a `DataTable`, [MergeObject](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/reference/txtextcontrol-documentserver/mailmerge/mergeobject-method/llms-full.txt) for a business object and [MergeObjects](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/reference/txtextcontrol-documentserver/mailmerge/mergeobjects-method/llms-full.txt) for a collection of them. The field names match the column names or the public properties.

A `MailMerge` component from the toolbox can also be connected to `textControl1` in the **Properties** window. Then `Merge` uses the document in the editor as the template and loads the result back into the editor. [Where the Merge Runs](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/mail-merge/overview/#where-the-merge-runs) describes this setup.

### Next Steps

- [Add Repeating Merge Blocks](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/getting-started/mail-merge/blocks/llms-full.txt): repeat a table row for each invoice item.
- [Data Sources](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/mail-merge/data-sources/llms-full.txt): JSON, business objects, DataSets and configuration files in detail.
- [Merge Events](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/mail-merge/events/llms-full.txt): change fields and blocks during the merge.

---

## Nearby

- **Previous:** [Create a Template](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/getting-started/mail-merge/template/llms-full.txt)
- **Next:** [Add Repeating Merge Blocks](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/getting-started/mail-merge/blocks/llms-full.txt)